US7244466B2 - Kinetic spray nozzle design for small spot coatings and narrow width structures - Google Patents

Abstract

An improved nozzle for use in kinetic spray systems is disclosed. The nozzle includes a supersonic portion comprising a tubular section and a flow regulator. A portion of the flow regulator is received in the tubular portion. The flow regulator includes a biconical flow concentrator that allows one to create very small dimension coatings on substrates. Using the present nozzle enables one to create spot coatings and very narrow width line coatings that find use in electrical components.

Description

TECHNICAL FIELD

The present invention is directed to a method for producing a coating using a kinetic spray system and an improved nozzle for use in the same. The improved nozzle permits one to spray a much smaller coating than previously possible. This improvement enables small spot coatings on narrow width line coatings.

INCORPORATION BY REFERENCE

U.S. Pat. No. 6,139,913, “Kinetic Spray Coating Method and Apparatus,” and U.S. Pat. No. 6,283,386 “Kinetic Spray Coating Apparatus” are incorporated by reference herein.

BACKGROUND OF THE INVENTION

A new technique for producing coatings on a wide variety of substrate surfaces by kinetic spray, or cold gas dynamic spray, was recently reported in a series of articles by T. H. Van Steenkiste et al., entitled “Kinetic Spray Coatings,” published in Surface and Coatings Technology, vol. 111, pages 62-71, Jan. 10, 1999. 386 and in “Aluminum coatings via kinetic spray with relatively large powder particles” published in Surface and Coatings Technology 154, pages 237-252, 2002. The articles discussed producing continuous layer coatings having low porosity, high adhesion, low oxide content and low thermal stress. The articles describes coatings being produced by entraining metal powders in an accelerated air stream, through a converging-diverging de Laval type nozzle and projecting them against a target substrate. The particles are accelerated in the high velocity air stream by the drag effect. The air used can be any of a variety of gases including air, nitrogen, or helium. It was found that the particles that formed the coating did not melt or thermally soften prior to impingement onto the substrate. It is theorized that the particles adhere to the substrate when their kinetic energy is converted to a sufficient level of thermal and mechanical deformation. Thus, it is believed that the particle velocity must be high enough to exceed the yield stress of the particle to permit it to adhere when it strikes the substrate. It was found that the deposition efficiency of a given particle mixture was increased as the inlet air temperature was increased. Increasing the inlet air temperature decreases its density and increases its velocity. The velocity varies approximately as the square root of the inlet air temperature. The actual mechanism of bonding of the particles to the substrate surface is not fully known at this time. It is believed that the particles must exceed a critical velocity prior to their being able to bond to the substrate. The critical velocity is dependent on the material of the particle and the substrate. It is believed that when the particles and the substrate are both metals then the initial particles to adhere to the substrate have broken the oxide shell on the substrate material permitting subsequent metal to metal bond formation between plastically deformed particles and the substrate. Once an initial layer of particles has been formed on a substrate subsequent particles bind not only to the voids between previous particles bound to the substrate but also engage in particle to particle bonds. The bonding process is not due to melting of the particles in the air stream because the temperature of the particles is always below their melting temperature, even when the temperature of the air stream is well above their melting temperature.

This work improved upon earlier work by Alkimov et al. as disclosed in U.S. Pat. No. 5,302,414, issued Apr. 12, 1994. Alkimov et al. disclosed producing dense continuous layer coatings with powder particles having a particle size of from 1 to 50 microns using a supersonic de Laval type nozzle.

The Van Steenkiste article reported on work conducted by the National Center for Manufacturing Sciences (NCMS) to improve on the earlier Alkimov process and apparatus. Van Steenkiste et al. demonstrated that Alkimov's apparatus and process could be modified to produce kinetic spray coatings using particle sizes of greater than 50 microns and up to about 106 microns.

This modified process and apparatus for producing such larger particle size kinetic spray continuous layer coatings are disclosed in U.S. Pat. Nos. 6,139,913, and 6,283,386. The process and apparatus provide for heating a high pressure air flow up to about 650° C. and combining this with a flow of particles. The heated air and particles are directed through a de Laval-type nozzle to produce a particle exit velocity of between about 300 m/s (meters per second) to about 1000 m/s. The thus accelerated particles are directed toward and impact upon a target substrate with sufficient kinetic energy to bond the particles to the surface of the substrate. The temperatures and pressures used are sufficiently lower than that necessary to cause particle melting or thermal softening of the selected particle. Therefore, no phase transition occurs in the particles prior to or during bonding. It has been found that each type of particle material has a threshold critical velocity that must be exceeded before the material begins to adhere to the substrate. The disclosed method did not disclose the use of particles in excess of 106 microns.

One difficulty associated with all of these prior art kinetic spray systems is that the particle stream exiting the nozzle rapidly expands so it has not been possible to form small discrete spots or narrow lines of coatings. Instead, the smallest spot coatings are approximately 2 millimeters by 10 millimeters. To achieve finer coatings it has been necessary to use masks. The use of masks is inconvenient and not always satisfactory. Thus, it is desirable to provide a method and apparatus to permit kinetic spraying of discrete small volume areas. Such applied coatings could be used. for example, for electrical contacts, wear points, insulating points in circuit boards and to trace circuits onto circuit boards.

SUMMARY OF THE INVENTION

In one embodiment, the present invention is a method for applying a coating by a kinetic spray method comprising the steps of: providing a powder of particles to be sprayed; providing a supersonic nozzle comprising an outer tubular section with an inner wall and a flow regulator with the flow regulator received inside the inner wall and a flow gap defined between the inner wall and the flow regulator; providing a heated main gas and entraining the particles in the main gas; directing the entrained particles through the gap thereby accelerating the particles and directing the accelerated particles toward a substrate positioned opposite the nozzle; and adhering the accelerated particles to the substrate to form a coating on the substrate.

In another embodiment, the present invention is a method of applying a coating by a kinetic spray method comprising the steps of: providing a powder of particles to be sprayed; providing a supersonic nozzle comprising an outer tubular section with an inner wall and a flow regulator with the flow regulator received inside the inner wall and a flow gap defined between the inner wall and the flow regulator; providing a heated main gas and passing the main gas through the gap; entraining the particles in the main gas after it passes through the gap thereby accelerating the particles and directing the accelerated particles toward a substrate positioned opposite the nozzle; and adhering the accelerated particles to the substrate to form a coating on the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a generally schematic layout illustrating a kinetic spray system for performing the method of the present invention;

FIG. 2 is an enlarged cross-sectional view of one embodiment of a kinetic spray nozzle designed in accordance with the present invention and used in the system;

FIG. 3 is an exploded cross-sectional view of the supersonic portion of the nozzle;

FIG. 4 is a cross-sectional view along line A-A ofFIG. 2;

FIG. 5 is a cross-sectional view along line B-B ofFIG. 3;

FIG. 6 is an enlarged cross-sectional view of another kinetic spray nozzle designed in accordance with the present invention and used in the system;

FIG. 7 is a cross-sectional view of another embodiment of a flow regulator designed in accordance with the present invention;

FIG. 8 is a cross-sectional view along line E-E ofFIG. 6;

FIG. 9 is a cross-sectional view along line F-F of Figure; and

FIG. 10 is a cross-sectional view of another embodiment of a tubular section designed in accordance with the present invention.

DESCRIPTION OF A PREFERRED EMBODIMENT

Referring first toFIG. 1, a kinetic spray system according to the present invention is generally shown at10.System10 includes anenclosure12 in which a support table14 or other support means is located. A mountingpanel16 fixed to the table14 supports awork holder18 capable of movement in three dimensions and able to support a suitable workpiece formed of a substrate material to be coated. Theenclosure12 includes surrounding walls having at least one air inlet, not shown, and anair outlet20 connected by asuitable exhaust conduit22 to a dust collector, not shown. During coating operations, the dust collector continually draws air from theenclosure12 and collects any dust or particles contained in the exhaust air for subsequent disposal.

Thespray system10 further includes agas compressor24 capable of supplying gas pressure up to 3.4 MPa (500 psi) to a high pressuregas ballast tank26. Thegas ballast tank26 is connected through aline28 to both a highpressure powder feeder30 and aseparate gas heater32. Thegas heater32 supplies high pressure heated gas, the main gas described below, to akinetic spray nozzle34. Thepowder feeder30 mixes particles of a spray powder with unheated high pressure gas and supplies the mixture to asupplemental inlet line48 of thenozzle34. Acomputer control35 operates to control both the pressure of gas supplied to thegas heater32 and the temperature of the heated main gas exiting thegas heater32. The gas can comprise air, helium, nitrogen, neon, argon, or mixtures thereof.

FIG. 2 is a cross-sectional view of one embodiment of anozzle34 and its connections to thegas heater32 and thesupplemental inlet line48. Amain gas passage36 connects thegas heater32 to thenozzle34.Passage36 connects with apremix chamber38 which directs the gas through aflow straightener40 and into a mixingchamber42. Temperature and pressure of the heated main gas are monitored by a gasinlet temperature thermocouple44 in thepassage36 and apressure sensor46 connected to the mixingchamber42.

The mixture of unheated high pressure gas and coating powder is fed through thesupplemental inlet line48 to apowder injector tube50 comprising a straight pipe having a predetermined inner diameter. Thetube50 has acentral axis52 which is preferentially the same as the axis of thepremix chamber38. Thetube50 extends through thepremix chamber38 and theflow straightener40 into the mixingchamber42.Particles100 exit thetube50 and are entrained in the main gas flow in the mixingchamber42.

Mixingchamber42 is in communication with asupersonic nozzle54 designed according to the present invention. Referring toFIGS. 2-5 thenozzle54 has atubular section56 and aflow regulator58. Thetubular section56 was aninner wall60 with a diameter sufficiently large enough to receive a portion of theflow regulator58 as is explained below. Thetubular section56 is shown inFIG. 3 as having a cylindrical inner and outer shape, however, the inner and outer shapes could be any shape as will be recognized by one of ordinary skill in the art. It is important that the shape of theinner wall60 allow for anannular flow gap78, as disclosed below.

Theflow regulator58 has abase portion62 with afirst half64 opposite asecond half66. Afirst cone68 projects from thefirst half64. A plurality ofholes70 are spaced around thecone68 and pass through thebase portion62. Aflow concentrator72 projects from thesecond half66. Theflow concentrator72 is biconical with asecond cone74 and athird cone76, the second andthird cones74,76 sharing a common base diameter D. The diameter D is less than a diameter of theinner wall60 at the point where they are adjacent to each other, as shown in the Figures. Thesecond half66 has a diameter that is less than a diameter of thefirst half64.

Thesecond half66 andflow concentrator72 are received in thetubular section56 with the diameter of thesecond half66 matching that of a diameter of theinner wall60. The difference in the diameter D and the diameter of theinner wall60 adjacent D defines anannular flow gap78. Preferably, the flow gap is from 1 to 5 millimeters with from 2 to 3 especially preferred. Thus, the diameter of theinner wall60 is from 2 to 10 millimeters greater than D and more preferably from 4 to 6 millimeters greater than D at the point where they are adjacent to each other.

In use ofnozzle54, theparticles100 are entrained in the main gas flow in the mixingchamber42 thefirst cone68 directs the entrainedparticles100 and main gas through theholes70 into thetubular portion56. Thesecond cone74 forces the flow of gas andparticles100 outward toward theinner wall60 and thegap78. Once the flow andparticles100 reach thegap78 the flow beyond the gap goes from sonic to supersonic. The shape of thethird cone76 and60, permit the main gas flow to force theparticles100 to follow the contour ofcone76 and concentrates theparticles100 into a well defined small spot. The main gas largely flows outside theparticle100 stream and forces them into a compact flow. This enables one to create narrow width lines or spots in the absence of a mask. In fact, using thenozzle54 of the present invention one can create spots having dimensions of 0.9 by 0.9 millimeters.

As discussed thepowder injector tube50 supplies a particle powder mixture to thesystem10 under a pressure in excess of the pressure of the heated main gas from thepassage36. Thenozzle54 produces an exit velocity of the entrainedparticles100 of from 200 meters per second to as high as 1200 meters per second. The entrainedparticles100 gain kinetic and thermal energy during their flow through thisnozzle54. It will be recognized by those of skill in the art that the temperature of theparticles100 in the gas stream will vary depending on the size of theparticles100 and the main gas temperature. The main gas temperature is defined as the temperature of heated high-pressure gas at the inlet to thenozzle54. The main gas temperatures are set so that theparticles100 are only heated to a temperature that is less than the melting point of theparticles100. This temperature can be substantially above the melting temperature of theparticles100. Temperatures can range from 200 to 1000 degrees Celsius. Because theparticles100 are exposed to these elevated temperatures for such a short period of time theparticles100 never reach their melting temperature. Thus, even upon impact, there is no change in the solid phase of theoriginal particles100 due to transfer of kinetic and thermal energy, and therefore no change in their original physical properties. Theparticles100 are always at a temperature below the main gas temperature. Theparticles100 exiting thenozzle54 are directed toward a surface of a substrate to coat it.

Upon striking a substrate opposite thenozzle54 theparticles100 flatten into a variety of nub-like structures with an aspect ratio of generally about 5 to 1. When the substrate is a metal and theparticles100 are a metal theparticles100 striking the substrate surface fracture the oxidation on the surface layer and subsequently form a direct metal-to-metal bond between themetal particle100 and the metal substrate. Upon impact the kinetic sprayedparticles100 transfer substantially all of their kinetic and thermal energy to the substrate surface and stick if their yield stress has been exceeded. As discussed above, for a givenparticle100 to adhere to a substrate it is necessary that it reach or exceed its critical velocity which is defined as the velocity where at it will adhere to a substrate when it strikes the substrate after exiting thenozzle54. This critical velocity is dependent on the material composition of theparticle100 and the substrate. In general, harder materials must achieve a higher critical velocity before they adhere to a given substrate. It is not known at this time exactly what is the nature of the particle to substrate bond; however, it is believed that a portion of the bond is due to theparticles100 plastically deforming upon striking the substrate.

As disclosed in U.S. Pat. No. 6,139,913 the substrate material may be comprised of any of a wide variety of materials including a metal, an alloy, a semi-conductor, a ceramic, a plastic, and mixtures of these materials. All of these substrates can be coated by the process of the present invention. The particles used in the present invention may comprise any of the materials disclosed in U.S. Pat. Nos. 6,139,913 and 6,283,386 in addition to other know particles. These particles generally comprise metals, alloys, semiconductors, ceramics, polymers, diamonds and mixtures of these. In the present invention one can utilizeparticles100 having a average nominal median diameter of from 1 to 200 microns, with 50 to 150 microns preferred and 50 to 125 microns especially preferred.

A second embodiment of a supersonic nozzle is shown generally at54′ inFIGS. 6-9. In this embodiment thetubular section56′ is elongated compared tonozzle54. Apowder injection tube50′ is elongated and extends through aflow regulator58′ to the tip ofthird cone76. The elongatedpowder injector tube50′ is received inside ahole120 inflow regulator58′. Preferably, the powder is injected at a pressure of from 100 to 150 psi using thisnozzle54′. The other parameters described above for the first embodiment,nozzle54, substrates, particles and main gas are equally useful for this embodiment. The other desirable modification is to elongate thetubular section56′ so it extends from 2.5 to 10 centimeters beyond the tip ofthird cone76. Theparticles100 are concentrated and focused by the main gas, which is supersonic after it passes through thegap78 to produce a spot concentration ofparticles100.

InFIG. 10 another embodiment of atubular section56″ is shown. In this embodiment thetubular section56″ includes afirst portion130 having a diameter sufficient to accommodate theflow regulator58,58′ and to define theannular gap78 between thefirst portion130 and theflow regulator58,58′ as described above. Thetubular section58″ further includes asecond portion132 that has a tapered shape. The tapered shape receives thethird cone76 of theflow regulator58,58′. Thissecond portion132 ends in anexit end134. Theexit end134 can have a variety of shapes including a rectangular shape, a circular shape, or a semi-circular shape. Thistubular section56″ can function to further concentrate the flow ofparticles100 as they exit from thenozzle54,54′.

The present invention permits one to create discrete spots on substrates and very narrow width lines. The spots have found use as electrical conductor points, wear points, and attachment points. The narrow width lines can be used to create electrical circuits and to coat very narrow width substrates.

While a preferred embodiment of the present invention has been described so as to enable one skilled in the art to practice the present invention, it is to be understood that variations and modifications may be employed without departing from the concept and intent of the present invention as defined in the following claims. The preceding description is intended to be exemplary and should not be used to limit the scope of the invention. The scope of the invention should be determined only by reference to the following claims.

Claims (35)

1. Applying a coating by a kinetic spray method comprising the steps of:

a) providing a powder of particles to be sprayed;

b) providing a supersonic nozzle comprising an outer tubular section with an inner wall and a flow regulator with the flow regulator received inside the inner wall and a flow gap defined between the inner wall and the flow regulator;

c) providing a heated main gas and entraining the particles in the main gas;

d) directing the entrained particles through the gap thereby accelerating the particles and directing the accelerated particles toward a substrate positioned opposite the nozzle; and

e) adhering the accelerated particles to the substrate to form a coating on the substrate.

2. The method as recited inclaim 1, wherein step a) comprises providing particles having an average nominal median diameter of from 1 to 200 microns.

3. The method as recited inclaim 1, wherein step a) comprises providing particles having an average nominal median diameter of from 50 to 150 microns.

4. The method as recited inclaim 1, wherein step a) comprises providing particles having an average nominal median diameter of from 50 to 125 microns.

5. The method as recited inclaim 1, wherein step a) comprises providing particles of a metal, an alloy, a semiconductor, a ceramic, a polymer, diamond or mixtures thereof.

6. The method as recited inclaim 1, wherein step b) comprises providing a flow regulator comprising a biconical flow concentrator formed from a second cone and a third cone sharing a common base with the flow gap defined by the space between the common base and the inner wall.

7. The method as recited inclaim 1, wherein step b) comprises providing a flow gap of from 1 to 5 millimeters between the inner wall and the flow regulator.

8. The method as recited inclaim 1, wherein step b) comprises providing a flow gap of from 2 to 3 millimeters between the inner wall and the flow regulator.

9. The method as recited inclaim 1, further comprising providing a plurality of holes through a base portion of the flow regulator and passing the entrained particles through the plurality of holes prior to directing the entrained particles through the gap.

10. The method as recited inclaim 1, wherein step c) comprises providing a heated main gas at a temperature of from 200 to 1000 degrees Celsius.

11. The method as recited inclaim 1, wherein step d) comprises accelerating the particles to a velocity of from 200 to 1200 meters per second.

12. The method as recited inclaim 1, wherein step e) comprises adhering the particles to a substrate comprising at least one of a metal, an alloy, a semi-conductor, a ceramic, a plastic, or a mixture thereof.

13. The method as recited inclaim 1, wherein step e) comprises forming a coating having a width of less than or equal to 1 millimeter.

14. The method as recited inclaim 1, wherein step e) comprises forming a coating having a width of less than or equal to 1 millimeter without using a mask or stencil.

15. The method as recited inclaim 1, wherein step e) comprises forming a spot coating having a diameter of less than or equal to 1 millimeter.

16. The method as recited inclaim 1, wherein step e) comprises forming a spot coating having a diameter of less than or equal to 1 millimeter without using a mask or stencil.

17. The method as recited inclaim 1, wherein step b) further comprises providing a tubular section having a first portion and a second portion with the second portion having a tapered shape.

18. Applying a coating by a kinetic spray method comprising the steps of:

a) providing a powder of particles to be sprayed;

b) providing a supersonic nozzle comprising an outer tubular section with an inner wall and a flow regulator with the flow regulator received inside the inner wall and the flow regulator comprising a biconical flow concentrator formed from a second cone and a third cone sharing a common base and a flow gap defined by the space between the common base and the inner wall;

c) providing a heated main gas and passing the main gas through the gap;

d) entraining the particles in the main gas after it passes through the gap thereby accelerating the particles and directing the accelerated particles toward a substrate positioned opposite the nozzle; and

e) adhering the accelerated particles to the substrate to form a coating on the substrate.

19. The method as recited inclaim 18, wherein step a) comprises providing particles having an average nominal median diameter of from 1 to 200 microns.

20. The method as recited inclaim 18, wherein step a) comprises providing particles having an average nominal median diameter of from 50 to 150 microns.

21. The method as recited inclaim 18, wherein step a) comprises providing particles having an average nominal median diameter of from 50 to 125 microns.

22. The method as recited inclaim 18, wherein step a) comprises providing particles of a metal, an alloy, a semiconductor, a ceramic, a polymer, diamond or mixtures thereof.

23. The method as recited inclaim 18, wherein the flow regulator further comprises a hole and the particles are passed through the hole prior to being entrained in the main gas.

24. The method as recited inclaim 18, wherein step b) comprises providing a flow gap of from 1 to 5 millimeters between the inner wall and the flow regulator.

25. The method as recited inclaim 18, wherein step b) comprises providing a flow gap of from 2 to 3 millimeters between the inner wall and the flow regulator.

26. The method as recited inclaim 18, further comprising providing a plurality of holes through a base portion of the flow regulator and passing the main gas through the plurality of holes prior to passing it through the gap.

27. The method as recited inclaim 18, wherein step c) comprises providing a heated main gas at a temperature of from 200 to 1000 degrees Celsius.

28. The method as recited inclaim 18, wherein step d) comprises accelerating the particles to a velocity of from 200 to 1200 meters per second.

29. The method as recited inclaim 18, wherein step e) comprises adhering the particles to a substrate comprising at least one of a metal, an alloy, a semi-conductor, a ceramic, a plastic, or a mixture thereof.

30. The method as recited inclaim 18, wherein step e) comprises forming a coating having a width of less than or equal to 1 millimeter.

31. The method as recited inclaim 18, wherein step e) comprises forming a coating having a width of less than or equal to 1 millimeter without using a mask or stencil.

32. The method as recited inclaim 18, wherein step e) comprises forming a spot coating having a diameter of less than or equal to 1 millimeter.

33. The method as recited inclaim 18, wherein step e) comprises forming a spot coating having a diameter of less than or equal to 1 millimeter without using a mask or stencil.

34. The method as recited inclaim 18, wherein step b) further comprises providing a tubular section having a first portion and a second portion with the second portion having a tapered shape.

35. Applying a coating by a kinetic spray method comprising the steps of:

a) providing a powder of particles to be sprayed;

b) providing a supersonic nozzle comprising an outer tubular section with an inner wall and a flow regulator with the flow regulator received inside the inner wall and a flow gap defined between the inner wall and the flow regulator and with the flow regulator including a base portion defining a plurality of holes through the base portion;

c) providing a heated main gas and passing the main gas through the plurality of holes prior to passing the main gas through the gap and passing the main gas through the gap;

d) entraining the particles in the main gas after it passes through the gap thereby accelerating the particles and directing the accelerated particles toward a substrate positioned opposite the nozzle; and

e) adhering the accelerated particles to the substrate to form a coating on the substrate.

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